1. Field of the Invention
The present invention relates to a scroll type compressor that is principally used in refrigeration and air conditioning systems for commercial and residential use.
2. Description of Related Art
Several types of electrical compressors are used for refrigeration and air conditioning, including a reciprocating type, a rotary type, and a scroll type. Each of these types has been developed considering the special characteristics of each type along with the cost and performance of the type. Among these, the scroll type compressor, which exhibits high efficiency, low noise, and low vibration, has come to be widely used.
Japanese patent Laid-open No. Hei.5-240176 describes a scroll compressor that uses one injection port which is connected to two compression chambers to perform the gas injection, so that the amount of gas injected into each chamber is equal. By this method, it is possible to avoid both heat deformation of the scroll parts due to localized thermal imbalance and lubricant degradation.
However, the increasing requirement to have many operation modes has made it necessary to be able to control the rotation speed of the scroll compressor using an inverter controller or similar device, which will allow the compressor to reach its optimum operation state. Another requirement that has come to be made is that the compressor be able to shutoff or resume gas injection as appropriate to the situation.
In the cases of variable speed rotation and gas injection shutoff or resumption conditions, since the conventional compressor always has a fixed compression ratio, the efficiency in the case of low speed operation is limited. Furthermore, if the gas injection is shutoff, there will be some coolant gas in dead volume areas that include the check valve that is in the area surrounding the gas injection port. This coolant gas, after being compressed in the compression chamber during the compression stage, will re-expand after the next coolant is brought into the compression chamber to begin confinement. This will have a large effect on the low load operation where the rotation speed is low, decreasing the performance.